This invention relates generally to halocarbon conversion and, more specifically, to the formation of hydrocarbons from halocarbons.
As the uncertain nature of ready supplies and access to crude oil has become increasingly apparent, alternative sources of hydrocarbons and fuel have been sought out and explored. The conversion of low molecular weight alkanes (lower alkanes) to higher molecular weight hydrocarbons has received increasing consideration as such low molecular weight alkanes are generally available from readily secured and reliable sources. Natural gas, partially as a result of its comparative abundance, has received a large measure of the attention focused on sources of low molecular weight alkanes. Large deposits of natural gas, mainly composed of methane, are found in many locations throughout the world. In addition, low molecular weight alkanes are generally present in coal deposits and may be formed during numerous mining operations, in various petroleum processes, and in the above- or below-ground gasification or liquefaction of synthetic fuelstocks, such as coal, tar sands, oil shale and biomass, for example. In addition, in the search for petroleum, large amounts of natural gas are discovered in remote areas where there is no local market for its use as a fuel or otherwise. Additional major natural gas resources are prevalent in many remote portions of the world such as remote areas of western Canada, Australia, U.S.S.R. and Asia. Commonly, natural gas from these types of resources is referred to as "remote gas".
Generally, much of the readily accessible natural gas is used in local markets as the natural gas has a high value use as a fuel whether in residential, commercial or industrial applications. Accessibility, however, is a major obstacle to the effective and extensive use of remote gas. In fact, vast quantities of natural gas are often flared, particularly in remote areas from where its transport in gaseous form is practically impossible.
Conversion of natural gas to liquid products is a promising solution to the problem of transporting low molecular weight hydrocarbons from remote areas and constitutes a special challenge to the petrochemical and energy industries. The dominant technology now employed for utilizing remote natural gas involves its conversion to synthesis gas, also commonly referred to as "syngas", a mixture of hydrogen and carbon monoxide, with the syngas subsequently being converted to liquid products. While syngas processing provides a means for converting natural gas to a more easily transportable liquid that in turn can be converted to useful products, the intermediate step involved in such processing, i.e., the formation of the synthesis gas, is typically relatively costly as it involves adding oxygen to the rather inert methane molecule to form a mixture of hydrogen and carbon monoxide. While oxygen addition to the carbon and hydrogen of methane molecules may be advantageous when the desired products are themselves oxygen containing, such as methanol or acetic acid, for example, such oxygen addition is generally undesirable when hydrocarbons such as gasoline or diesel fuel are the desired products as the added oxygen must subsequently be removed. Such addition and removal of oxygen naturally tends to increase the cost involved in such processing.
Methane, the predominant component of natural gas, although difficult to activate, can be reacted with oxygen or oxygen-containing compounds such as water or carbon dioxide to produce synthesis gas. Synthesis gas can be converted to syncrude such as with Fischer-Tropsch technology and then upgraded to transportation fuels using usual refining methods. Alternatively, synthesis gas can be converted to liquid oxygenates which in turn can be converted to more conventional transportation fuels via catalysts such as certain zeolites.
Because synthesis gas processing requires high capital investment, with the syngas being produced in relatively energy intensive ways, such as by steam reforming where fuel is burned to supply heat for reforming, and represents an indirect route to the production of hydrocarbons, the search for alternate means of converting methane directly to higher hydrocarbons continues.
One such alternative method involves methane conversion to higher hydrocarbons via a "chlorine-assisted" route, such as represented by the following 2-step process: EQU CH.sub.4 +HCl+O.sub.2 .fwdarw.chloromethanes+H.sub.2 O (1) EQU chloromethanes.fwdarw.C.sub.2+ hydrocarbons+HCl (2)
In the first step of such a process, methane (using HCl and oxygen) is chlorinated to chloromethanes. Such a chlorination step is also referred to as methane "oxychlorination" or "oxyhydrochlorination."
In the second step of such a process, chloromethanes are converted to higher hydrocarbons, e.g., hydrocarbons having 2 or more carbon atoms, represented by "C.sub.2+ ", and HCl. The HCl generated in the second step can be recycled back to the first step so that effectively there is no net consumption of chlorine in the overall process.
Such a chlorine-assisted process is not yet practiced commercially.
Brothy, et al., U.S. Pat. No. 4,652,688 and Brothy, et al., U.S. Pat. No. 4,665,270 disclose processes for the conversion of monohalomethanes to hydrocarbons having at least two carbon atoms. In Brothy, et al. '688, the monohalomethane is contacted with a synthetic crystalline gallosilicate zeolite loaded either with at least one modifying cation of hydrogen, metals of Groups I to VIII of the periodic table, or with a compound of at least one Group I to VIII metal. In Brothy, et al. '270, the monohalomethane is contacted with a synthetic crystalline aluminosilicate zeolite having a silica to alumina molar ratio of at least 12:1 and containing cations of either hydrogen, copper or a metal capable of forming an amphoteric oxide, which cations are introduced either by exchange and/or by deposition, provided that when the cation is hydrogen the zeolite is Theta-1.
Butter, et al., U.S. Pat. No. 3,894,017 discloses a process for the conversion of alcohols, mercaptans, sulfides, halides and/or amines to desirable products such as aromatic hydrocarbons as well as other higher molecular weight hydrocarbons. The process utilizes a crystalline aluminosilicate zeolite catalyst having a high silica to alumina ratio of at least about 12 and a constraint index of about 1 to 12. The catalyst also preferably has a crystal density in the hydrogen form of not substantially less than about 1.6.
C. E. Taylor and R. P. Noceti, in a presentation entitled "A Process For Conversion Of Methane To Higher Hydrocarbons" presented at the 6th DOE Indirect Liquefaction Contractors' Conference in Monroeville, Pennsylvania, Dec. 3-4, 1986 reported that ZSM-5 is effective for chloromethane conversion to liquid hydrocarbons.
Noceti, et al., U.S. Pat. No. 4,769,504, discloses a process for the production of aromatic-rich, gasoline boiling range hydrocarbons from lower alkanes, particularly from methane. The process is carried out in two stages. In the first stage, an alkane is reacted with oxygen and hydrogen chloride over an oxyhydrochlorination catalyst such as copper chloride with minor proportions of potassium chloride and rare earth chloride. This produces an intermediate gaseous mixture containing water and chlorinated alkanes. In the second stage, the chlorinated alkanes are subsequently contacted with a crystalline aluminosilicate catalyst in the hydrogen or metal promoted form to produce gasoline range hydrocarbons with a high proportion of aromatics and a small percentage of light hydrocarbons (C.sub.2 -C.sub.4). The light hydrocarbons can be recycled for further processing over the oxyhydrochlorination catalyst.
Imai, et al., U.S. Pat. No. 4,795,843 disclose treating methane with a haliding agent, such as chlorine, bromine or iodine to form a methyl halide which subsequently may be converted into usable products by contacting the halides with a conversion catalyst of silicalite, a particular type of crystalline silica material. Such a catalyst is disclosed as being less active than a crystalline aluminosilicate having a silica to alumina ratio of about 20:1 but has improved stability relative to such a crystalline aluminosilicate.
The search for alternative catalysts effective in catalyzing the conversion of halocarbons, in particular, chlorocarbons and especially chloromethanes to liquid hydrocarbons has, however, continued.
Catalytically active, crystalline borosilicate sieve catalyst is the subject of commonly assigned Klotz, U.S. Pat. No. 4,268,420; Klotz, U.S. Pat. No. 4,269,813; Klotz, et al., U.S. Pat. No. 4,285,919 and Published European Application No. 68,796. These patents disclose the preparation, characterization and utility of crystalline borosilicate catalyst and are hereby incorporated by reference.
As described in the references in the paragraph above, catalyst compositions typically are formed by incorporating an AMS-1B crystalline borosilicate molecular sieve material into a matrix such as alumina, silica or silica-alumina to produce a catalyst formulation. In one method of making AMS-1B crystalline borosilicate, sieve material is formed by crystallizing sources for silicon oxide and boron oxide with sodium hydroxide and an organic compound. After crystallization, the resulting sodium form is ion exchanged with an ammonium compound and calcined to yield the hydrogen form of AMS-1B. In another more preferred method, AMS-1B crystalline borosilicate is crystallized in the hydrogen form from a mixture containing a diamine in place of a metal hydroxide. AMS-1B borosilicates in hydrogen form are designated HAMS-1B. Typically, the hydrogen form sieve is gelled with an alumina sol, dried and calcined to yield a catalyst composition.
None of these patents, however, disclose or suggest the use of crystalline borosilicate sieve catalyst in a process for the conversion of halocarbons and, in particular, chlorocarbons to hydrocarbons.